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From: Jonathan Ellis <jbellis@gmail.com>
Date: Thu, 7 Jul 2011 21:27:36 -0500
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 <CALdd-zjXazQHLBDgzS5c_fAko8Qn6UeeorigSqR1HcSgiAVu2w@mail.gmail.com>
Subject: Re: What does a write lock ?
To: user@cassandra.apache.org
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Sounds to me like you're confusing atomicity with isolation.

On Thu, Jul 7, 2011 at 2:54 PM, Jeffrey Kesselman <jeffpk@gmail.com> wrote:
> Yup, im even more confused. =A0 =A0Lets=A0talk=A0about the model, not the
> implementation.
> AIUI=A0updates=A0to a row are atomic across all columns in that row at on=
ce,
> true?
> If true then the next question is, does the validation happen inside or
> outside of that=A0guarantee, and is the row=A0guaranteed=A0not to=A0chang=
e between
> validation and update?
> If that is *not* the case then it makes a whole class of=A0solutions=A0to
> synchronization problems fail and puts my larger project
> in=A0serious=A0question.
>
> On Thu, Jul 7, 2011 at 3:43 PM, Yang <teddyyyy123@gmail.com> wrote:
>>
>> no , the memtable is a concurrentskiplistmap
>>
>> insertion can happen in parallel
>>
>> On Jul 7, 2011 9:24 AM, "Jeffrey Kesselman" <jeffpk@gmail.com> wrote:
>> > This has me more confused.
>> >
>> > Does this mean that ALL rows on a given node are only updated
>> > sequentially,
>> > never in parallel?
>> >
>> > On Thu, Jul 7, 2011 at 3:21 PM, Yang <teddyyyy123@gmail.com> wrote:
>> >
>> >> just to add onto what jonathan said
>> >>
>> >> the columns are immutable . if u overwrite/ reconcile a new obj is
>> >> created and shoved into the memtable
>> >>
>> >> there is a shared lock for all writes though which guard against an
>> >> exclusive lock on memtable switching/flushing
>> >> On Jul 7, 2011 7:51 AM, "A J" <s5alye@gmail.com> wrote:
>> >> > Does a write lock:
>> >> > 1. Just the columns in question for the specific row in question ?
>> >> > 2. The full row in question ?
>> >> > 3. The full CF ?
>> >> >
>> >> > I doubt read does any locks.
>> >> >
>> >> > Thanks.
>> >>
>> >
>> >
>> >
>> > --
>> > It's always darkest just before you are eaten by a grue.
>
>
>
> --
> It's always darkest just before you are eaten by a grue.
>


--=20
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com